A triangular threading insert has a mount portion (60) with three sides forming locating faces (50, 52, 54) that lie on the three sides of an imaginary triangle (96) and has three cutting arms (21-23) with outer edges (80) for cutting threads. The outer edge of each arm projects sidewardly beyond the sides of the imaginary triangle, to leave locating faces of long length. The top face (110) of the mount portion forms a hexagon with the cutting arms projecting radially from three of the sides (71-73) of the hexagon, and with the other three sides of the hexagon extending parallel to the locating faces of the mount portion. Each locating face has a smaller height (H) than the thickness (T) of the insert, with concave border regions merging the top and bottom (124, 126) of each locating face to the top and bottom faces of the insert, and merging horizontally-spaced ends (134, 136) of each locating face to a cutting arm.
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2. A cutting apparatus comprising:
an insert having a mount portion with three locating sides lying on the sides of an imaginary triangle that has a triangle axis, said insert having a radially outwardly extending arm at each of three corner portions of the triangle, with each arm having an outer cutting edge and a pair of opposite arm sides that extend in a primarily radially outward direction with respect to said axis; each of said arms has a location that projects beyond a side of said imaginary triangle; each of the opposite arm sides at each arm has an arm side inner end (134, 136) that is furthest from the cutting edge of the arm, and each of said locating sides extends substantially straight along the entire distance between the arm side inner ends of two different arms; said mount portion has a vertically-extending locating face lying on each of said triangle sides; each of said locating sides has horizontally-spaced and primarily vertically-extending ends, and each of said locating sides forms a primarily vertically elongated concave border where each locating face end merges with a side of one of said arms.
1. A cutting apparatus comprising:
an insert having a mount portion with three locating sides lying on the sides of an imaginary triangle that has a triangle axis, said insert having a radially outwardly extending arm at each of three corner portions of the triangle, with each arm having an outer cutting edge and a pair of opposite arm sides that extend in a primarily radially outward direction with respect to said axis; each of said arms has a location that projects beyond a side of said imaginary triangle; each of the opposite arm sides at each arm has an arm side inner end (134, 136) that is furthest from the cutting edge of the arm, and each of said locating sides extends substantially straight along the entire distance between the arm side inner ends of two different arms; said mount portion has top and bottom horizontal planar faces that are vertically spaced by a predetermined insert thickness (T), and said locating sides have planar side location faces lying in vertical planes when said triangle axis is vertical, with each locating face having a height (H) that is less than said insert thickness, and with each triangle side having horizontally-elongated borders lying between the top of the locating face and the mount portion top face, and between the bottom of the locating face and mount portion bottom face, with said borders being concave.
3. A cutting apparatus comprising:
an insert having a mount portion with three locating sides lying on the sides of an imaginary triangle that has a triangle axis, said insert having a radially outwardly extending arm at each of three corner portions of the triangle, with each arm having an outer cutting edge and a pair of opposite arm sides that extend in a primarily radially outward direction with respect to said axis; each of said arms has a location that projects beyond a side of said imaginary triangle; each of the opposite arm sides at each arm has an arm side inner end (134, 136) that is furthest from the cutting edge of the arm, and each of said locating sides extends substantially straight along the entire distance between the arm side inner ends of two different arms; a bar that is elongated along a bar axis for insertion into a workpiece hole, said bar axis extending in front and rear directions, said bar having a front end with an insert-holding recess having a flat bottom wall, and said insert-holding recess having first and second positioning surfaces angled 60°C from each other, with a first of said positioning surfaces angled 60°C to said bar axis; said insert lies in said insert-holding recess, with a first of said arms which is positioned to cut, projecting radial to said triangle axis and also projecting perpendicular to said bar axis, with said first arm outer edge extending parallel to said bar axis.
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The economical machining of internal threads in a small diameter bore of a workpiece, can be accomplished by mounting a triangular shape insert in a corresponding pocket of a bar or the like. Then the bar is fed into the bore of the workpiece. When a cutting edge of the insert becomes worn, a fastener is loosened, the insert is rotated 120°C, and the fastener is retightened with a fresh cutting edge positioned to cut a thread. The insert has a horizontal bottom surface and a pair of vertical locating surfaces that are tightly clamped to corresponding positioning surfaces in the pocket of the tool holder bar. The clamped surfaces are intended to provide stability for the insert to resist deflection and avoid vibration under the very high forces encountered during thread cutting. Although the bottom location surface comprises a large area, the side locating surfaces of prior art inserts are less than adequate due to the thread form being ground into the sides of a triangular shape insert blank. The insufficient locating surface remaining, is subjected to very high forces per unit area where it presses against corresponding positioning surfaces of the tool holder pocket. If the area of the locating surface could be increased, for a triangular insert of predetermined size (i.e. which can fit into a hole of predetermined size) then threads could be cut with a much smaller possibility of damage due to excess forces between the insert locating surfaces and the tool holder positioning surfaces.
For ease in machining, the locating surfaces on the insert and the corresponding positioning surfaces in the pocket of the tool holder are machined flat. It can be appreciated that the insert should be constructed so its locating surfaces can be easily ground precisely flat, and that the flatness and the angles between the different locating surfaces can be easily measured.
In accordance with one embodiment of the present invention, a threading insert of generally triangular shape and with three cutting arms is provided, wherein a mount portion of the insert, from which the arms project, forms long locating surfaces, where the locating surfaces can be easily precisely machined and measured. The mount portion has triangle sides lying on the sides of an imaginary triangle that has an axis, with each cutting arm extending generally radially outward from the mount portion and having an outer edge adjacent to a corner of the imaginary triangle. The outer edge of each arm has a location that projects beyond the side of the imaginary triangle. As a result, the insert of the present invention can not be readily ground from a blank of triangular shape, as in the prior art. Instead the present insert is produced from a special blank of a special preformed shape.
The locating sides at the three triangle sides of the mount each has a height less than the total height of the mount, with the top and bottom of each locating side connected by a concave border to the upper and lower faces of the mount. Also, horizontally spaced opposite ends of each locating surface are each connected by a concave border to an arm. This results in each locating face being distinctly separated from surrounding portions of the insert. The upper face of the mount portion is preferably formed in a hexagon shape with substantially equal hexagon sides.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.
The locating surfaces 50, 52, 54 lie on the sides 90, 92, 94 of an imaginary triangle 96. In accordance with one feature of the invention, the arms, and particularly the outer edges 80 have portions 100, 102 that project beyond the sides of the imaginary triangle. In the past, triangular inserts were formed by first forming a triangular blank (as by pressing and sintering microscopic particles of tungsten alloy powder in a die), with the threading insert formed by grinding away a minimum of selected areas of the blank. This left the sides of the arms within the confines of the imaginary triangle which defined the shape of the original blank. For arms of given length, this resulted in a mount portion having locating sides of small length. Locating sides of small length result in a reduced area of contact between the locating sides of the insert (e.g. 50, 52 in
Applicant constructs the insert 14 of a blank that is machined (e.g. by grinding) so the locating surfaces 50, 52, 54 lie on the imaginary triangle 96, but portions 100, 102 of the arms project beyond the sides of that imaginary triangle. A result is that the sides of the mount portion 60 that lie on the imaginary triangle and that form the locating surfaces, can be made longer and the radially inner ends 104 of the cutting arms can be made wider. The longer locating surfaces such as 50 of length A result in high forces encountered during cutting being distributed over a larger area, reducing the possibility of damage to the tool holder or insert. The wider cutting arm inner end 104 results in less possibility of break off of the arm during thread cutting. It should be noted that the insert is tri-symmetric about the axis 64, so all three 120°C sectors 105-107 are identical.
In an insert that applicant has constructed and successfully tested, the insert had an overall maximum horizontal length B (
The insert had a thickness T (
Thus, the invention provides a threading apparatus, especially for cutting internal threads (or even grooves) in relatively small holes such as less than 30 mm, which provides large area locating surfaces with respect to the overall dimensions of the insert, and with the locating surfaces being easily manufactured with high precision. The insert has a mount portion with sides lying on an imaginary triangle, with locating surfaces on the sides of the triangle, and with arms adjacent to the corners of the triangle extending beyond the sides of the imaginary triangle. Each locating surface has top and bottom ends that are connected by elongated horizontal concave borders to the corresponding top and bottom faces of the mount portion of the insert. The mount portion has an upper face in the form of a hexagon whose six sides are of substantially uniform length.
Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.
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Nov 22 2000 | Tooling Specialties, Inc. | (assignment on the face of the patent) | / |
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